A brain-computer interface (BCI) is a system which is intended to permit a user to control an application/device by using only his or her thoughts (more specifically, using neuro-physiological signals detected from the brain or from other nervous tissue). BCI systems are typically based on an electroencephalography (EEG) recorded from the scalp. The EEG is measured and sampled while the user imagines different things (for example, moving the left hand or the right hand). Depending on the BCI, particular preprocessing and feature extraction methods are applied to an EEG sample of a certain length, with goal being to reliably detect the limited mind states from the EEG signals or patterns from the EEG samples with a certain level of accuracy.
A problem that arises, based at least in part on the limited understanding of the human brain and its inherent electrical activities, is that the accuracy of mind state detection is degraded as the number of mind states is increased. For example, at present it is not possible to recognize words that a user may think of (as might be desirable in order to implement a dictation task). However, the current state of the art does generally permit a few emotional states and/or motor intentions to be reliably detected, such as relaxed vs. stressed modes, moving the right hand, moving the left hand, and so forth.
The problem of constructing a reliable BCI has received considerable attention in recent years. Using EEG signals as a non-invasive method has been demonstrated to be a feasible approach in BCI. However, and as was noted above, due to the limited understanding of human brain and its electrical activities only a limited number of brain or mind states, driven by either physical or imagined actions, can be reliably detected, such as wake/sleep modes, motor-related EEG changes, and emotional states to some degree.
Previous studies have focused on applying EEG signals to simple command control tasks, for example moving a cursor on a computer screen or controlling movement of a robot or robot manipulator. This type of command-control has been implemented in a linear manner, i.e., the BCI control is structured to detect a subject's mind state from an EEG and to convert the detected mind state into a corresponding command. As can be appreciated, this type of simple linear control can become problematic when dealing with more complex tasks.